Fluorescent Lamps and Ballasts
There are multitudinous installations of fluorescent lamps in buildings throughout the world. The fluorescent lamp provided more uniform illumination and less costly operation than incandescent bulbs having a primary illumination filament that would burn out sooner than a typical fluorescent lamp. A fluorescent lamp consists of a glass tube filled with an inert gas (usually argon) at low pressure. On each side of the glass tube is an electrode. Electricity is passed through the gas, causing an arc of illumination. The glass tube is fitted into a fixture having sockets that receive electrode pins at an end of the glass tube. The sockets are sized to accept different standard diameter tubes, such as T12 (old and inefficient) with a diameter of 1.5 inches, T8 (higher in efficiency than T12) with 1 inch diameter). Both T12 and T8 lamps use the same medium bi-pin base, which allows T8 lamps to fit into the same fluorescent luminaire fixture as T12 lamps of the same length.
To get the fluorescent lamp started a spike of high voltage is needed to get the arc started. The colder the lamp is, the higher voltage that is needed to start the arc. The voltage drives current through the argon gas. Gas has an electrical resistance—the colder the gas, the higher the resistance, and the higher the voltage required to start the arc. Since creating a high voltage can be hazardous and expensive, ways were found to pre-heat the fluorescent lamp in order to require less voltage to start the lamp. There are different ways to start a lamp including: preheat, instant start, rapid start, quick start, semi-resonant start and programmed start. All of these require electronics which are part of a ballast for the lamp. An electrical ballast is a device that intended to limit the amount of current in an electric circuit. The ballast for a fluorescent lamp limits the current through the tube, which would otherwise rise to destructive levels due to the tube's negative resistance characteristic. A fluorescent (gas-discharge) lamp is an example of a device having negative resistance, where after lamp ignition, the increasing lamp current tends to reduce the voltage fed across it. The resistance equals the voltage divided by the current (Ohms Law). The resistance is therefor decreased if the voltage decreases or if it stays constant while the current increases. The resistance is thus lowered by increases in current (negative resistance). A simple series current limiting reactor (inductor) can effectively be the ballast for a lamp. However most modern ballasts have complex (expensive) electronics to control precisely the current or the voltage supplied to a fluorescent lamp. The lamp's ballast regulates the required alternating current (AC) electrical power delivered via the electrodes of the lamp. The ballast is typically physically located in a box mounted near its lamp or lamps. Older lamps used a separate starter to get the lamp' arc going. Modern lamps use an electrical pulse start which is delivered to the lamp by components within the ballast.
Historically, fluorescent lamps use AC power, effectively meaning that the electrode that functions as the cathode switches back and forth. If the lamp was DC, the cathode side would be brighter and more intense than the anode side since there are more free electrons spewing off of the (typically tungsten) electrode that performs as the cathode, and that side would become weaker as it lost atoms, causing the lamp to not last compared to an AC fluorescent lamp. Using AC, the electrons/ions leave one side of the lamp for the other but on the next (alternate) cycle go back. With AC, the lamp tube has a practically uniform brightness on both ends.
As electrical current forms an arc through the lamp, it ionizes a higher percentage of the tube's contained gas molecules. The more molecules that are ionized, the lower the resistance of the gas. If too many gas molecules are ionized, the resistance will drop to the point that an electrical short would occur. Therefore, the ballast also contains electronic components that control the current, preventing the current through the lamp from rising to the point that the lamp would burn out. Electronic ballasts use semiconductors to limit power to a fluorescent lamp. First the ballast rectifies the AC power, then it converts to a high frequency for improved efficiency. Electronic ballasts typically change the frequency of power to a lamp from 50/60 Hz to about 20 kHz. A modern electronic ballast can more precisely control power than an older magnetic ballast.
Types of Ballasts
Modern ballasts vary considerably in type and complexity. An instant start ballast does not preheat the electrodes, instead using a relatively high voltage (˜600 V) to initiate the discharge arc. It is the most energy efficient type of ballast, but results in the fewest on and off cycles for the lamp tube, as molecules of material is lost from the surface of the lamp tube's cold electrodes each time the lamp is turned on. Instant-start ballasts are used for applications with long duty cycles, in buildings the fluorescent lamps are not frequently turned on and off. Instant start lamps have a single pin (the cold cathode), and a high voltage spike is used to start the lamp. In contrast, a rapid start ballast is used for fluorescent lamps having a filament (two electrode pin lamp) that is used for pre-heating before the lamp is started. A rapid start ballast applies voltage and heats the two electrode pins (the cathodes) simultaneously. The rapid start ballast provides superior lamp life and more cycle life, but uses slightly more energy as the cathodes in each end of the lamp continue to consume heating power as the lamp operates. Because a 2-pin lamp is used with a ballast that preheats a filament for the electrode pins prior to starting the lamp, a lower voltage suffices to then start the lamp. A programmed-start ballast is a more advanced version of the rapid start ballast. The T5 lamp specification calls for a programmed-start, that provides precise heating of lamp filaments and controls the pre-heat time before the startup voltage is applied, thereby reducing filament stress. The programmed-start ballast applies power to the filaments first, which allows the cathodes to preheat and then applies voltage to the lamps to strike an arc. Lamp life typically operates up to 100,000 cycle life with programmed start ballasts. Once started, the programmed-start ballast's filament voltage is reduced to increase operating efficiency. This ballast gives the best life and most starts from lamps, and so is preferred for applications with very frequent on/off switching. Programmed start ballasts heat the electrodes first, reducing the shock to the lamp, maximizing both lamp and ballast life. Programmed start ballasts are the most expensive, but may be cost-effective by reducing lamp deterioration.
Shunted and NonShunted Sockets
It can be difficult to determine whether a fluorescent lamp fixture has an instant-start ballast or a rapid start ballast without locating the ballast and looking at its wiring diagram, which is usually affixed to the ballast. An instant-start has only wire coming from the ballast to one of the lamp end's socket, with the pins of that socket connected electrically (shunted). A rapid-start ballast has two wires coming from the ballast to one end of the lamp end's socket, with the pins of that socket not connected electrically (non-shunted). The lamp fixture often has two sockets facing either other, adapted to receive a straight lamp tube. The two pins of an Non-shunted socket connected to the ballast are for receiving power while the corresponding pins on the other socket are for physically securing the tube only. Many manufacturers use the same-looking socket for both shunted and Non-shunted sockets, with only a hidden wire doing the shunting if present. A shunted ballast merely connects two of the pins at either end of the lamp, whereas an Non-shunted ballast will bring the contact from each of two pins out to a separate connection back to the ballast. Counting both sockets (one at each end of the fluorescent fixture (lampholder)), a shunted lampholder will generally have 2 holes (or accept 2 wires) on the unit whereas an non-shunted lampholder will have 4 holes (or accept a total of 4 wires) on the unit. Ballast bypass requires cutting the wires between the ballast and the lamp socket, and re-routing the electrical supply wires from the input side of the ballast directly to the lamp socket. It may also entail physical detachment and removal of the unused ballast from the premises. In the case of ballasts that are physically remote from the lamp fixture, this can be especially time-consuming. Determining the kind of ballast system, shunted or Non-shunted, and identifying the status of wires connected to fluorescent fixture due for replacement with an LED tube can be time-consuming. There may be fluorescent fixtures that have been either neglected or prepared previously for LED replacement by having the ballast already removed, without any indication on the fixture of this status, and determining the status can also result in expense in the absence of the present invention.
Disadvantages of Fluorescent Lighting
Notwithstanding their advantages over incandescent light bulbs, fluorescent lamps have a number of problems. The fluorescent lamps can be highly efficient, but poorly made older ballasts can release noxious gases upon overheating. Electromagnetic ballasts with a minor fault can produce an audible humming or buzzing noise. Magnetic ballasts are usually filled with a tar-like compound to reduce emitted noise. The tar can melt or release gas. Hum is eliminated in lamps with a high-frequency electronic ballast, but even modern electronic ballasts can fail due to overheating. Additionally, fluorescent lamps emit a small amount of ultraviolet (UV) light. Fluorescent lamps with older magnetic ballasts flicker at a normally unnoticeable frequency of 100 or 120 Hz but this flickering can cause problems for some individuals with light sensitivity. Sensitive people may experience health problems that is aggravated by artificial lighting. The ultraviolet light from a fluorescent lamp can even adversely affect paintings, requiring that artwork be protected with transparent glass or acrylic filters. Fluorescent lamps generate harmonic currents in the electrical power supply within the ballast. The arc itself within the lamp generates radio frequency noise, which can be transmitted through power wiring. Radio signal suppression is available, but adds to the cost of the fluorescent fixtures. Fluorescent lamps operate optimally at typical room temperatures. At other temperature ranges, whether hotter or colder, efficiency decreases. At below-freezing fluorescent lamps may not start. Regarding outdoor use, fluorescent lamps do not generate as much heat as incandescent lamps and may not sufficiently melt snow or ice on the lamp, reducing illumination. If the lamp is frequently switched on and off, the lamp will rapidly age, because each start cycle slightly erodes the electron-emitting surface of the cathodes—when all the emission material is used up, the lamp cannot be started with the available ballast voltage. If a fluorescent lamp is broken, a very small amount of mercury can contaminate the surrounding environment. The broken glass itself is a hazard.
Replacement of Fluorescent Lighting with LEDs
For all the above reasons, there has been over the past decade an enormous commercial move toward replacing both incandescent and fluorescent light fixtures with light-emitting diode (LED) lighting. Arrays of LEDs can be fitted in tubes that are physically compatible replacement for fluorescent tubes, using the same sockets for their electrodes to fit into.
LEDs have advantages over those prior light sources: lower energy consumption, longer life, improved robustness, smaller size, and the ability to be switched on and off faster. Some LEDs can achieve full brightness in under a microsecond. LEDs emit more lumens per watt than incandescent light bulbs and most fluorescent tubes. LED lighting efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes. LEDs can be used that emit light of an intended color without using the filters that incandescent or fluorescent lighting would require to achieve the same effect. LED tube lights are available in different lengths with both clear and frosted lens styles, in a selection of 3000K, 4000 k or 5000K color temperatures, depending on whether visibly “cool” or “warm” lighting is desired. LEDs can easily be dimmed either by pulse-width modulation or lowering the current to them, whereas fluorescent lamps can require expensive circuitry to dim, and many use older ballasts that cannot provide dimming at all, the ballast requiring a standard (undimmed) input of AC power. Unlike other light sources, LEDs designed for visible light illumination radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED. LED lights require no warm up time, require virtually no maintenance, and have a long life expectancy. Eventual failure of LEDs occurs usually by dimming over time, rather than the sudden failure of incandescent bulbs, or the unpleasant erratic output of failing fluorescent lamps and ballasts. LED arrays can have 35,000 to 50,000 hours of life, compared to typical ratings for fluorescent tubes typically of 10,000 to 15,000 hours, depending on the ambient conditions, and for incandescent light bulbs typically of only 1,000 to 2,000 hours. Reduced maintenance costs from the use of LEDs with their extended lifetime, rather than energy savings, is often the more significant factor in determining the payback advantage for switching to LED lighting. LEDs are light weight and extremely durable as they are solid-state components, which are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile. To summarize, LED lights are eco-friendly lights that require no ballast, and offer maximum light output and energy savings. Compared to conventional fluorescent lamps, replacement can save more than 50% of the energy use, which pays for the replacement over time.
LEDs for general room lighting require more precise current and heat management than compact fluorescent lamp sources of comparable output. A light-emitting diode (LED) is a two-lead semiconductor light source. When a fitting voltage is applied to the leads, electrons combine with electron holes within the device, releasing energy as photons. This effect is called electro luminescence, and the color of the emitted light corresponds to the energy of the photon, controlled by the energy band gap of the semiconductor. The current-voltage characteristics of an LED is like other diodes, that is, the current is dependent exponentially on the voltage. A small change in voltage causes a large change in current. If the supplied voltage exceeds the LED's forward voltage drop by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. A solution is to use constant-current power supplies to keep the current below the LED's maximum current rating. Most LED fixtures drawing from AC wall receptacle power must have a driver circuitry that includes a power converter with at least a current-limiting resistor.
Replacing either an instant-start, shunted socket fluorescent lamp or a rapid-start non-shunted socket fluorescent lamp with a replacement LED tube and driver has previously required the ballast to be electrically detached or physically removed from the system, and the standard AC power wires to be attached directly to the driver's circuitry. Detachment can be expensive, typically requiring the services of a licensed electrician. Removal can also be time-consuming, requiring access to the ballast itself, which is often behind lamp fixture or ceiling panels.
To summarize, a fluorescent tube lamp requires a means to limit current flow to prevent a self-destroying positive feedback loop. The most common means to regulate current flow is to use an inductive ballast; consequently ballasted fluorescent fixtures are ubiquitous in the lighting industry. With the advent of power efficient high intensity LED lighting arrays, which have lumen output and power efficiencies on par with or exceeding fluorescent tube lamps, a need exists for replacement LED tube lamps that can accept power from to existing fluorescent fixtures with little or no additional adjustment. One should be able to plug an LED tube lamp into any size compatible fluorescent fixture (with or without ballast or shunt) and have the internal circuitry utilize the supplied energy to power the LED array. The known prior art solutions include using direct line voltage to power a secondary LED power supply while bypassing ballasted input power or physically removing the ballast altogether. Other solutions use back up battery power to supply the LED array, again bypassing the original ballasted input supply. None of the existing LED tube replacement lamps can be directly supplied from fluorescent fixtures with different configurations such as with or without ballasts, or with or without shunts. Existing methods are complex, inefficient, often requiring a separate power supply, and they are not adaptable to different fixture configurations.